A freestanding GaN substrate over 2 inches in size was successfully prepared for the first time by hydride vapor phase epitaxy (HVPE) using GaAs as a starting substrate. In the experiment, a GaAs (111)A substrate with a SiO2 mask pattern on its surface was used. A thick GaN layer was grown on the GaAs substrate at 1030°C through the openings in the SiO2 mask. By dissolving the GaAs substrate in aqua regia, a freestanding GaN substrate about 500 µm thick was obtained. The full-width at half maximum (FWHM) in the ω-mode X-ray diffraction (XRD) profile of GaN (0002) plane was 106 arcsec. The dislocation density of the GaN substrate obtained was determined to be as low as 2×105 cm-2 by plan-view transmission electron microscopy (TEM). Hall measurements revealed the n-type conductivity of the GaN substrate with typical carrier concentration and carrier mobility of 5×1018 cm-3 and 170 cm2V-1s-1, respectively.

Preparation of Large Freestanding GaN Substrates by Hydride Vapor Phase Epitaxy Using GaAs as a Starting Substrate : Semiconductors

The experimental investigation of the non-steady-state photoelectromotive force in aluminium nitride crystal is reported. The experiments are performed for two geometries, where arising photocurrent is parallel or perpendicular to the optical axis of the crystal. Dependencies of the signal amplitude versus light intensity, temporal and spatial frequencies are measured. The photoelectric parameters of the material are estimated for the light wavelength λ = 532 nm.

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P5 - Non-steady-state photoelectromotive force in AlN crystal

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Non-steady-state photoelectromotive force in AlN crystal

We report our observation of the photorefractive effect in undoped aluminum nitride. We measured the coupling constant and the formation rate as a function of pump intensity at a wavelength of 405 nm in a two-wave mixing experiment. The photorefractive gain coefficient was 0.47 cm−1 at I = 6.9 W/cm2, and the actual saturated value was probably larger than this. The time constant was 59 ms at I = 1.0 W/cm2. In addition to a refractive index grating, an absorption grating was also formed, which is attributed mainly to an ionized trap density modulation process.

Toru Nagai

Papers

Photorefractive effect in undoped aluminum nitride.